The overall goal of this project is to develop a panel of monoclonal antibodies specific for the PTH receptor. Immunogens to induce these antibodies will consist of intact cells which express relatively high concentrations of PTH receptors. Three different cultured cell lines will be used; UMR-106 rat osteoblastoma cells (UMR), differentiated F9 mouse embryonal carcinoma cells (F9), and immortalized opossum kidney cells (OKC).